With today's emphasis on ergonomics, products are being designed with the user's comfort in mind. Products such as chairs for the office are becoming more and more user friendly, in that they can be adjusted to a variety of positions to suit the individual needs or preferences of the user. Because of the ergonomic need for adjustability, many types of pivoting and damping mechanisms have been developed for use on chairs and other end assemblies.
One such device is described in U.S. Pat. No. 2,560,181 to Morvice in which a chair's reclining back 5 is mounted by brackets 9 and 10 which are pivotally connected by bolt 11. A torsion spring 18 resiliently connects brackets 9 and 10 to return the chair back to its original orientation. A friction disk 27 is pressed tightly against the bearing portion 23 of bracket 10 by a coiled compression spring 29. This friction force creates a restraining force to keep the seat back from springing back too quickly. However, there is no adjustment or locking available.
U.S. Pat. No. 3,195,952 to Bache et al. describes a seat with an infinitely adjustable inclining back wherein an arcuate slot 14 receives a bolt shaft within and the seat back 2 and the back pivots about the axis of a torsion bar 3. Holding pads 18 of friction elements act against sectors 13 of bracket and can be actuated by a lever 26 operated by the user to position the seat in any position. Although this device allows adjustment, these are complex components requiring multiple friction pads and are difficult to assemble; in addition, there is the possibility the friction pads will be improperly adjusted or will wear and the chair back will return to its upright position too abruptly.
U.S. Pat. No. 3,747,888 to Heckett describes an adjustable fluid pivot device. The device comprises an adjustable control wheel 20 for adjusting the level of compression of spring 26 by rotating tension block 16. Blades 34 rotate through a viscous fluid 36 to provide the rotational damping. However, this device lacks the capacity to lock.
U.S. Pat. No. 4,062,587 to Wolters describes a chair back positioning device comprising clutch plates 24 and 25 and wing plates 23 made of nylon and adjusted by lock and release handle 43. This device allows ease of adjustment, and some damping for providing controlled return of the seat back. However, this device is very complex, expensive, and difficult to assemble. Furthermore, the possibility of misadjustment and wear may, over time, cause the chair back to spring back too abruptly. Since seat adjustment is normally performed with the user seated in the chair, this abrupt return to full upright position may cause back injury.
U.S. Pat. No. 4,219,234 to Bell describes a chair back mechanism which utilizes dogs 80 and 82 that are actuated into engagement with arcuate slot 245 to lock seat back in position. However, this mechanism is too complex and also susceptible to wear.